The burden of proof is on you. You have to prove that the money you are remitting into Thailand comes from savings. Which is very difficult obviously. What I am trying to tell you is that you won't win in such a situation, unless you are extremely well prepared. Don't expect to just put the burden of proof on them, it is not how it works.
Sorry but the burden of proof is on you, not on them. So good luck to anybody trying to prove that the money comes from savings, not income. Unless they don't have any income at all of course.
, I would not want to apply with a sponsorship letter. We've seen some people getting their visa this way, but it sounds quite risky to me. I think the sponsorship letter thing on the online form is mostly for dependents, children and spouses, etc.
Hopefully your employer is established in one of the countries mentioned. Otherwise you'll have to go through double legalization of the biz registration. It's probably not even doable in 14 days which is the time you're given to upload requested documents.
No idea about Dubai, sorry. However, if you applied on June 5th, you haven't waited for a long time yet. It's been like 5 or 6 working days, assuming there was no holiday.
Of course you have to show financial evidence again, and you may be requested to show 1 million bahts, depending on the embassy. Actually if you start completing the online form, you can see a list of required document in the last page.
Go there, contact a Thai language school and apply for an extension of stay based on studying Thai every 3 months. You won't get a DTV for studying Thai. Expect to pay 30-55K bahts per year depending on where you want to study, and you'll have to leave Thailand every ~12 months if you want to stay longer than a year. Please note that you will have to genuinely study Thai, otherwise the immigration office may decide to deny further extensions.